Drilling an oil or gas well involves several steps prior and after a well is put into production. Primary oil-recovery operations include drilling the well, cementing the casing to the formation and completing the well prior to oil or gas production. Workover operations may be necessary during remedial work in producing wells, usually as an attempt to enhance or prolong the economic life of a well. When flow rate of the oil or gas is diminished, the reservoir of the well may be treated in some manner to increase the flow of oil or gas into the wellbore. This operation is called secondary recovery, known as fracturing/stimulation operations.
Fracturing/stimulation operations are performed either by acid wash or hydraulic fracturing. When the reservoir is depleted, enhanced oil recovery operations may be needed to increase the well's production rate. This operation is called tertiary recovery, and involves injection of fluids into the formation surrounding the production well to increase the flow rate of the formation fluid into the wellbore.
In order to accomplish the above mentioned operations, drilling fluids are used as an integral element of drilling programs for primary oil recovery. They are especially designed to perform numerous functions that are critical to the success of drilling operations. In order to perform these functions, drilling fluids should possess particular properties with regard to their rheology, density, and filtration control.
Guar and guar derivatives are widely used in fluids for use in oil-well fracturing and stimulation applications. They are particularly used in hydraulic fracturing fluids, to provide filtration control and rheology to suspend proppant, which are sized particles mixed with the hydraulic fracturing fluid and are used to hold fractures open after a hydraulic fracturing treatment, and carry the proppant into the fractured formation. They are used in combination with several other chemicals, and particularly crosslinkers to provide optimum crosslinked gels, necessary to suspend the proppant.
The ultimate viscosity of guar is heavily dependent on the quality of guar splits. While a few changes in the process may contribute to enhance the ultimate viscosity by a small amount, a main contributor remains the quality of the raw material. Over the past few years, a guar (Variety 365, a variety of guar seeds grown in irrigated regions such as Haryana in India) has been commercialized, and has been used to produce “high viscosity” guars. Such a high quality of guar is now imported to the USA, and all the majors pumping companies have adopted its use.
To produce such a high viscosity guar, the use of the newly engineered guar splits is not sufficient enough to fully extract the optimum viscosity potential out of the splits. Adjustment of process parameters is required. Laboratory experiments did highlight the importance of the initial wetting and tempering conditions to produce enhanced ultimate guar viscosity. However, many of the process changes would require a significant capital investment to consistently produce the desired high viscosity guar.
The product of the oxidation of aqueous solutions of guar gum and other galactose bearing polysaccharides using galactose oxidase enzyme was disclosed in U.S. Pat. No. 3,297,604, incorporated herein by reference in its entirety. The aldehyde bearing oxidized products are separated by precipitation from the aqueous solutions used for the enzyme reactions. U.S. Pat. No. 3,297,604 disclosed the use of the oxidized products in the manufacture of paper. The aldehyde bearing oxidized products were disclosed to be also suitable for use to crosslink polyamino polymers, polyhydroxy polymers, and proteins.
U.S. Pat. No. 5,554,745, incorporated herein by reference in its entirety, discloses (1) the preparation of cationic galactose containing polysaccharides and (2) the enzymatic oxidation in aqueous solution of the cationic galactose containing polysaccharides with galactose oxidase. The oxidized cationic polysaccharides are disclosed to improve the strength characteristics of paper.
U.S. Pat. No. 6,022,717, incorporated herein by reference in its entirety, discloses a process for the oxidation of the oxidizable galactose type of alcohol in oxidizable galactose type of alcohol configuration containing polymer, such as guar, with galactose oxidase in the presence of oxidation promoting chemicals. This patent does not disclose the use of such oxidized polymers in oilfield servicing fluids.
U.S. Pat. No. 6,124,124, incorporated herein by reference in its entirety, discloses a composition of an oxidizable galactose type of alcohol configuration containing polymer, such as guar, which is in solid state and galactose oxidase. Application of such oxidized polymers in the papermaking process results in superior paper strength characteristics. This patent does not disclose the use of such oxidized polymers in oilfield servicing fluids.
U.S. Pat. No. 6,179,962, incorporated herein by reference in its entirety, discloses a process for making paper having improved strength characteristics by adding to the pulp water-soluble and/or water-dispersible cationic polymer and oxidized galactose type of alcohol configuration containing polymer, such as guar. This patent does not disclose use of such oxidized polymer in oilfield servicing fluids.
U.S. Patent 2003/0054963 discloses a method of treating a subterranean formation using a well-treated fluid where the gelling agent includes a fast hydrating, high-viscosity guar powder. This patent does not disclose any galactose oxidase treatment to enhance the viscosity of the guar.
U.S. Pat. No. 6,884,884 discloses a method for depolymerizing galactomannan and derivatives thereof with a liquid cleaving agent. This patent describes the cleaving agents as a chemical molecule that non-specifically cleaves ether bonds between mannoses in the galactomannan backbone which includes acids such as hydrogen halides in the form of a liquid (acid hydrolysis) and oxidizing reagents (oxidative degradation) but does not include enzymes. Among the objects of this patent is to provide a method for making a composition comprising galactomannan having a certain molecular weight, polydispersity index and viscosity, which is useful, e.g., in treating or making a fracture in a subterranean formation.
High viscosity is an important aspect to the crosslinked gels. To increase efficiency over commercially available guars, there is still a need for even higher viscosity polymers that would allow the use of reduced polymer loading to minimize the level of residue after break, hence increasing the return permeability.